The objective of this project is to characterize and clarify, from cellular to molecular level, the mechanism of activation of phospholipase A2 in a rat mast cell line, rat basophilic leukemia (RBL-2H3) cells. Therefore, my main goals are: 1. To determine whether release of arachidonic acid in RBL-2H3 cells is dependent on activation of existing phospholipase A2 or expression of new enzyme. 2. To identify isozymes of phospholipase A2 in RBL-2H3 cells and to prepare the antibodies to them. 3. To determine whether phospholipase A2 can be activated via G- proteins and/or tyrosine phosphorylation.